Is it possible to use four corners of a single marker for a plane track?
Using Python, we can just create a new track for each of the corners, which in turn allows to create a classical Plane Track.

  tracking = D.movieclips['clip.avi'].tracking
  begin, end = C.scene.frame_start, C.scene.frame_end
  corners = [tracking.tracks.new(frame=begin) for i in range(4)]
  track = tracking.tracks['Track']
  for frame in range(begin, end+1):
     track_marker = track.markers.find_frame(frame)
     for i, corner in enumerate(corners):
        corner.markers.insert_frame(frame)
        corner_marker = corner.markers.find_frame(frame)
        corner_marker.co = track_marker.pattern_corners[i]
        corner_marker.co += track_marker.co


However, this is quite clumsy a solution.